Mellon Square is an urban park in downtown Pittsburgh. The park is built above a parking garage, and features a distinctive tree-lined black-and-white geometric pavement, fountains, raised flower beds and a cascading waterfall. Mellon Square Park is one of the city's most prominent gathering spots.

The square occupies an entire city block, bounded by Smithfield Street, William Penn Place, Oliver and Sixth Avenues. It is surrounded by many prominent downtown buildings, including the Oliver Building, 525 William Penn Place, the William Penn Hotel, and the Alcoa Building (Regional Enterprise Tower). In addition to the undergound parking, the Mellon Square complex also houses retail shops along Smithfield Street.

Mellon Square was conceived in the late-1940s. After World War II, the Alcoa Company (American Aluminum Company of America), which was established in the late 19th century with financial backing from the Mellon Family, considered a move to New York. Banker Richard King Mellon aimed to block the move, and proposed a new downtown headquarters building for the company, then known as the Alcoa Building and now called the Regional Enterprise Tower.

In another move made in part to entice Alcoa to remain in Pittsburgh, on April 22, 1949, the A. W. Mellon Educational and Charitable Trust, Sarah Mellon Scaife, and Richard King Mellon Foundation announced a gift to the City of Pittsburgh of $4 million (later boosted to $4.3 million) to build the 1.37-acre Mellon Square Plaza, designed by architects Mitchell and Ritchey of Pittsburgh.

  
The future location of Mellon Square Plaza was a mix of old buildings and street-level parking lot.

  
A city block worth of buildings were demolished to make way for the Mellon Square Plaza and parking garage.

As a bonus, Alcoa employees would have an underground parking garage capped by the public plaza. On September 28, 1953, at 12:15pm, ground was broken by members of the Mellon family and Mayor David Lawrence. On that same day, Pittsburgh City Council officially renamed the entire city block "Mellon Square".

Construction of Mellon Square took shortly over two years. At the peak of construction, several hundred Pittsburgh workers were employed on the project. First came three layers of waterproofing. Then varying layers of sand and gravel and cement fill. This was covered with four inches of concrete including a built-in snow-melting system.

  
The construction of Mellon Square Plaza took two years and a cost of $4,500,000.

More than 1,250 tons of reinforcing steel was used. Braces kept streets from possible cave-ins. Enough material was hauled out of the square to fill the equivalent of 540 boxcars and enough concrete was poured into the hole to pack ninety boxcars solid.

The underground parking has a capacity of 900 cars. Above ground, the square was decorated with over 25,000 trees, shrubs and flowers. The nine circular bronze basins for the block-long fountain were, in 1953, the largest ever cast.

  
Mellon Square nears completion (left) and the official Dedication Day on October 18, 1955.

When construction of Mellon Square Plaza was completed, the Mellon family gave the property to the City of Pittsburgh. The square is named in honor Richard Beatty Mellon (1858-1933) and Andrew Mellon (1855-1937).

The park was officially dedicated on October 18, 1955. The total cost of $7.8 million far exceeded the original $4,500,000 estimate. For the Mellons, the added expense was worth it to create such an attractive urban refuge.

In addition to the creation of Mellon Square, Richard King Mellon's concern over other proposed corporate moves, including Westinghouse and U.S. Steel, prompted other inner city modernization efforts in the 1940s and 1950s during the Renaissance I years. These including the Gateway Center Complex and the adjacent Point State Park. The stunning expanse of office towers and urban plazas became known as "Mellon's Miracle."

Today, over half a century after opening, the plazas along "Mellon's Miracle" along Commonwealth Avenue, and Mellon Square Plaza on Smithfield Street, are still some of Pittsburgh's signature gathering places, small oasis' in the heart of the city.